George Clooney is preparing his Studio City mansion for President Barack Obama's arrival.

Security for tonight's event is at an all-time high ... with the LAPD Bomb Detection K-9 unit doing a full sweep of the area. In addition to the bomb squad, the CHP and the U.S. Secret Service will also be present.

The Ocean's Eleven actor will welcome the commander-in-chief for a $40,000-per-plate fundraising event. 150 A-list guests and their deep pockets have been invited to attend the black tie affair.

Clooney is expected to raise up to $12 million in donations for Obama's campaign, which officially makes this one of the biggest presidential fundraisers in U.S. history, according to The Hollywood Reporter.

Obama, who recently said "same-sex couples should be able to get married," has plans to be back in LA on June 6 for a Lesbian, Gay, Bisexual and Transgender gala.